1. Field of the Invention
The invention relates to the field of radiation therapy systems. One embodiment includes an active path planning and collision avoidance system to facilitate movement of objects in a radiation therapy environment in an efficient manner and so as to proactively avoid possible collisions.
2. Description of the Related Art
Radiation therapy systems are known and used to provide treatment to patients suffering a wide variety of conditions. Radiation therapy is typically used to kill or inhibit the growth of undesired tissue, such as cancerous tissue. A determined quantity of high-energy electromagnetic radiation and/or high-energy particles are directed into the undesired tissue with the goal of damaging the undesired tissue while reducing unintentional damage to desired or healthy tissue through which the radiation passes on its path to the undesired tissue.
Proton therapy has emerged as a particularly efficacious treatment for a variety of conditions. In proton therapy, positively charged proton subatomic particles are accelerated, collimated into a tightly focused beam, and directed towards a designated target region within the patient. Protons exhibit less lateral dispersion upon impact with patient tissue than electromagnetic radiation or low mass electron charged particles and can thus be more precisely aimed and delivered along a beam axis. Also, upon impact with patient tissue, protons exhibit a characteristic Bragg peak wherein a significant portion of the kinetic energy of the accelerated mass is deposited within a relatively narrow penetration depth within the patient. This offers the significant advantage of reducing delivery of energy from the accelerated proton particles to healthy tissue interposed between the target region and the delivery nozzle of a proton therapy machine as well as to “downrange” tissue lying beyond the designated target region. Depending on the indications for a particular patient and their condition, delivery of the therapeutic proton beam may preferably take place from a plurality of directions in multiple treatment fractions to maintain a total dose delivered to the target region while reducing collateral exposure of interposed desired/healthy tissue.
Thus, a radiation therapy system, such as a proton beam therapy system, typically has provision for positioning a patient with respect to a proton beam in multiple orientations. In order to determine a preferred aiming point for the proton beam within the patient, the typical procedure has been to perform a computed tomography (CT) scan in an initial planning or prescription stage from which multiple digitally reconstructed radiographs (DRRs) can be determined. The DRRs synthetically represent the three dimensional data representative of the internal physiological structure of the patient obtained from the CT scan in two dimensional views considered from multiple orientations. A desired target isocenter corresponding to the tissue to which therapy is to be provided is designated. The spatial location of the target isocenter can be referenced with respect to physiological structure of the patient (monuments) as indicated in the DRRs.
Upon subsequent setup for delivery of the radiation therapy, an x-ray imager is moved into an imaging position and a radiographic image is taken of the patient. This radiographic image is compared or registered with the DRRs with respect to the designated target isocenter. The patient's position is adjusted to, as closely as possible, align the target isocenter in a desired pose with respect to the radiation beam as indicated by the physician's prescription. The desired pose is frequently chosen as that of the initial planning or prescription scan. Depending on the particular application, either the patient and/or the beam nozzle will need to be moved.
There is a desire that movement of components of the therapy system to achieve alignment be done in an accurate, rapid manner while maintaining overall system safety. In particular, a radiation therapy apparatus is an expensive piece of medical equipment to construct and maintain both because of the materials and equipment needed in construction and the indication for relatively highly trained personnel to operate and maintain the apparatus. In addition, radiation therapy, such as proton therapy, is increasing being found an effective treatment for a variety of patient conditions and thus it is desirable to increase patient throughput both to expand the availability of this beneficial treatment to more patients in need of the same as well as reducing the end costs to the patients or insurance companies paying for the treatment and increase the profitability for the therapy delivery providers. As the actual delivery of the radiation dose, once the patient is properly positioned, is relatively quick, any additional latency in patient ingress and egress from the therapy apparatus, imaging, and patient positioning and registration detracts from the overall patient throughput and thus the availability, costs, and profitability of the system.
The movable components of a radiation therapy system also tend to be rather large and massive, thus indicating powered movement of the various components. As the components tend to have significant inertia during movement and are typically power driven, a safety system to inhibit damage and injury can be provided. Safety systems can include power interrupts based on contact switches. The contact switches are activated at motion stop range of motion limits to cut power to drive motors. Hard motion stops or limiters can also be provided to physically impede movement beyond a set range. However, contact switches and hard stops are activated when the corresponding component(s) reach the motion limit and thus impose a relatively abrupt motion stop which adds to wear on the machinery and can even lead to damage if engaged excessively. In addition, particularly in application involving multiple moving components, a motion stop arrangement of contact switches and/or hard limiters involves significant complexity to inhibit collision between the multiple components and can lead to inefficiencies in the overall system operation if the components are limited to moving one at a time to simplify the collision avoidance.
From the foregoing it will be understood that there is a need for providing a collision avoidance system to maintain operating safety and damage control while positioning multiple movable components of a radiation therapy delivery system. There is also a desire to maintain the accuracy and speed of the patient registration process when implementing such a collision avoidance system.